Google Earth was recently updated. It now includes Google Sky which lets you virtually gaze into the heavens with a virtual telescope complete with place names and restaurant locations. What you didn't know was that they also built a flight simulator in.
Start Google Earth. <= Make sure you have the latest version available at earth.google.com
If necessary, close the tips.
Some people have reported that Ctrl+Alt+A doesn't work but have got it going with Ctrl+A or Ctrl+Windows+A
You may also find the option "Enter Flight Simulator..." under the "Tools" menu.
A choice of aircraft are presented to you. An F16 fighter jet or a SR22 prop plane. Choose and airport and start flight.
It supports joysticks so if you have one, try it out.
Google have supplied online help with a list of keyboard commands to help you control your aircraft.
Cool, fly around the world. For free. Yay!